1. In stock pot, add onion and sauté in a few tablespoons olive oil until soft. Add celery (including leaves) and sauté for a few minutes more.
2. Add water, veggie bouillon, potatoes, and approximately a dozen whole parsley sprigs. Simmer covered for about 1 hour.
3. Let cool and refrigerate overnight. To finish soup, remove parsley sprigs and liquefy in food processor. Add milk and reheat slowly being careful not to boil, as it will separate the milk.
4. Add fresh chopped parsley, salt and pepper to taste. Add more diced celery if you prefer more texture.
This soup is surprisingly flavorful for being so simple. If you find you have a bunch of celery leftover from another recipe, this is great use for it. The more celery you use in this soup the more celery flavor you will get. You can make this soup without it resting overnight but the flavor will be weak. Pairs nicely with crusty bread.